import java.util.Arrays;
import java.util.Scanner;

/**
 * 
 */

/**
 * @author zhongfang
 *
 */
public class 网易1 {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		Scanner scanner=new Scanner(System.in);
		int n=scanner.nextInt();
		int A[] =new int[n];
		for (int i = 0; i < n; i++) {
			A[i]=scanner.nextInt();
		}
		Arrays.sort(A);
		int d=A[1]-A[0];
		boolean poss=true;
		for (int i = 2; i < n; i++) {
			int diff=A[i]-A[i-1];
			if(diff!=d){
				poss=false;
				break;
			}
		}
		if(poss){
			System.out.println("Possible");
		}else {
			System.out.println("Impossible");
		}
	}

}
